ARM: fix the calculation of the values in the RV clocks

This clock is used by the linux scheduler.

src/dev/arm/rv_ctrl.cc

@@ -65,12 +65,12 @@ RealViewCtrl::read(PacketPtr pkt)
         break;
       case Clock24:
         Tick clk;
-        clk = (Tick)(curTick() / (24 * SimClock::Int::us));
+        clk = SimClock::Float::MHz * curTick() * 24;
         pkt->set((uint32_t)(clk));
         break;
       case Clock100:
         Tick clk100;
-        clk100 = (Tick)(curTick() / (100 * SimClock::Int::us));
+        clk100 = SimClock::Float::MHz * curTick() * 100;
         pkt->set((uint32_t)(clk100));
         break;
       case Flash: